Originally Posted by
Roll-Monroe-Co
All the Schwinn SNs with which I'm familiar are on the head tube (or head badge) or on the right drop out. So I'm thinking that what you're looking at is a part ID number.
FWIW, My 1984 Schwinn le tour has the serial number on the bottom bracket shell; it's a Greenville, Mississippi built Schwinn. The serial number starts with "SG4"